This invention relates to rotatable polygon mirrors for use with laser beam scanning apparatus including means for handling and storing a mirror.
An Ar.sup.+ ion laser generates a beam often used in laser beam scanning apparatus for transferring information from a stationary document to an imaging station. This beam is converted in the apparatus to a modulated beam and an unmodulated beam by optical elements. By scanning the unmodulated beam, a stationary document may be read at a reading station. An element for receiving diffuse beam reflections from the stationary document converts the variation in intensity of the reflections into electrical signals which represent the information on the document. The modulated beam, which is modulated by these electrical signals, is scanned to record an image on the imaging station. The image is developed and the developed image is transferred to a copy medium.
In the past, a galvanomirror scanner has been used to scan the beam. The galvanomirror has planar reflecting mirrors and the mirrors rotate around an axis within a certain rotation angle. Since the oscillatory period of the galvanomirror was limited according to the mechanics of it, the scanning speed was limited.
Instead of the galvanomirror, a rotatable polygon mirror may be used to increase the scanning speed. As is well-known, a polygon mirror includes a solid body having a cross section in the form of a regular polygon. The mirror has a plurality of reflecting flat facets for scanning the beam, the facets being successively turned through a position perpendicular to the axis of the polygon.
It is very important to handle the polygon mirror without touching the reflecting facets when it is being carried or mounted to a shaft of a motor. It is troublesome therefore when the polygon portion of a polygon mirror is grasped or touched during such handling.
If the centroid of the polygon mirror does not coincide with its axis, the mirror will vibrate during its rotation. Vibration of the mirror during rotation causes inaccurate scanning. Accordingly, it is necessary that the polygon mirror be rotated on the shaft of the motor without any eccentricity. It is difficult to adjust for any eccentricity in the rotation of the polygon mirror, for example, by mounting a balance weight on the shaft of the motor.
In case of manufacturing a plurality of polygon mirrors, the mirror forms are stacked with each polygon end in the direction of the axis of the polygon. When the facets of the polygon mirrors are then cut with a cutter, shavings tend to be left between the facets of the polygon mirrors. Accordingly, the outer edges of the facets can not be properly sharpened, the shavings causing roughness on the outer edges of the facets. Considerable difficulty, therefore, has arisen in the simultaneous manufacture of a number of polygon mirrors.